1. Field of the Invention
This invention relates to solutions of perfluorinated copolymers. The solutions of this invention are particularly related to perfluorinated copolymers of tetrafluoroethylene and perfluorinated sulfonyl fluoride- or carboxyl-containing vinyl monomer of equivalent weight greater than about 1000. Those copolymers have many uses including uses as membrane material in liquid permeation processes such as electrolysis, dialysis, and reverse osmosis. Solutions of the present invention can be used to make such membranes or to repair membranes already made. Such solutions can also be used to coat support materials to provide an efficient catalyst.
2. Discussion of the Prior Art
Ionic fluorocarbon copolymers such as the copolymers of ethylene and sulfonyl fluoride- or carboxyl-containing vinyl monomer mentioned above have been known for many years. For example, U.S. Pat. No. 3,282,875 issued Nov. 1, 1966 discloses such copolymers. U.S. Pat. No. 3,692,569, issued Sept. 19, 1972 discloses such copolymers and discloses that the copolymer materials can be formed by being extruded, cast, or molded. That patent discloses certain halogenated solvents for the copolymer such as ortho-dichlorobenzene, symmetrical trichlorobenzene, and perfluorokerosene; and discloses that solutions of the copolymer using those solvents occurs at above 130.degree. C. and preferably above 170.degree. C.
The sulfonyl fluoride fluoropolymers of high equivalent weight have proven difficult to dissolve at moderate conditions, such as at temperatures of about 20.degree. to 30.degree. C. below the copolymer melting point. U.S. Pat. No. 4,038,213 issued July 26, 1977 discloses that finely-divided particles of sulfonic acid-containing fluoropolymer can be dissolved in ethanol, but there is no disclosure of the solution of sulfonyl fluoride-containing fluoropolymers.
British Pat. No. 1,286,859 published Aug. 23, 1972 specifically discloses the difficulty of preparing solutions of such ionic copolymers and stands as a teaching of the tortuous means required for making a solution of such ionic fluoropolymers prior to the discovery of this invention. In that British patent, sulfonyl fluoride groups on fluorocarbons having equivalent weights less than 1000, are converted to sulfonic acid or sulfonamide. The sulfonic acid or amide form of fluoropolymers having relatively low equivalent weight is somewhat soluble in hydrocarbon alcohols of up to four carbon atoms.
German Preliminary Published Appl. No. 2,510,071 published Sept. 11, 1975 and U.S. Pat. No. 4,065,366 issued Dec. 27, 1977 disclose carboxyl-containing fluoropolymers having high equivalent weight which, in the methyl ester form, could be made into the solutions of this invention.